Leptospermone

Leptospermone is a chemical compound (a β-triketone) produced by some members of the myrtle family (Myrtaceae), such as Callistemon citrinus (Lemon Bottlebrush), a shrub native to Australia, and Leptospermum scoparium (Manuka), a New Zealand tree from which it gets its name.^[1] Modification of this allelopathic chemical to produce mesotrione led to the commercialization of derivative compounds as HPPD inhibitorherbicides.

Leptospermone was first identified in 1927 and was extracted from a variety of plants in 1965, 1966 and 1968. It was first identified as a chemical in Callistemon citrinus in California in 1977. A biologist at the Western Research Centre of Stauffer Chemical Company noticed that very few plants grew under Callistemon citrinus bushes. After taking soil samples and creating an array of extracts, one was identified as an herbicide. While it did have herbicidal effects, the rate required for sufficient coverage was too high to be of practical use.^[2]

Leptospermone was optimized into thousands of compounds. Several were extremely effective but were too toxic, environmentally persistent or not selective enough. There are now several members of the triketone class of HPPD inhibitor herbicides on the market.^[3][4]

Leptospermone can be synthesized from phloroglucinol by a reaction with 3-methylbutanenitrile (isovaleronitrile) in the presence of a zinc chloride catalyst. Phloroisovalerone imine is produced which is then alkylated with iodomethane after initial treatment with sodium ethoxide and methanol to produce an intermediate which is treated with aqueous hydrochloric acid resulting in isovaleroylsyncarpic acid (leptospermone).^[5]

Bioquímicamente, las plantas adoptan un enfoque diferente . A pesar de que la síntesis bioquímica no se ha investigado específicamente, está claro que la leptospermona no es un terpeno oxidado (o específicamente un sesquiterpeno , es decir, C ₁₅ ), ya que la ciclación del pirofosfato de farnesilo no puede producir dos carbonos dimetilados separados por un solo carbono, ni esto sería consistente con la aparición natural de compuestos similares con diferentes cadenas laterales ceto-arílicas en los miembros de Myrtaceae ( por ejemplo, flavesona, papuanona, isoleptospermona y grandiflorona ^{[ 1 ]} ). El floroglucinol se biosintetiza en un solo paso a partir de malonil-CoA ^{[ 6 ]} y podría ser el intermediario, pero pueden ser posibles otras rutas de biosíntesis, como a través de isobutiril-CoA , el resultado de la condensación descarboxilativa de cetoisovalerato (forma cetónica de valina ) (cf. policétidos ).

La leptospermona fue el modelo para el compuesto mesotriona , que tiene el nombre comercial Callisto , un herbicida de Syngenta . ^{[ 4 ]}